Fuel metering device especially for the combustion chamber of an aerojet engine

ABSTRACT

A fuel metering device comprises a metering needle guided cantilever fashion in a bore and operated by a double-acting actuator so as to regulate the passage cross-section of a regulating aperture which determines the flow rate under pressure of a fuel containing or possibly containing solid impurities. The control consists of a piston integral with a shaft of the needle and sliding inside a cylinder, and the bore is made through a partition separating this cylinder from a chamber receiving the regulated fuel flowing out of the regulating aperture. The two chambers of the cylinder are fed, at modulated pressures, with filtered fuel, and the bore is provided with an annular groove which is fed with fuel taken through a filter upstream of the metering device.

Mar. 4, 1975 United States Patent 1 Grunert et al.

FUEL METERING DEVICE ESPECIALLY X 8 A 5 2 6 l 7 3 l 5 XX 5 N w H7 3 1 7.

J m mam N W .ooawwom CCLTCR 578007-3 666677 gwgggg NUWUWM 440774 063930 3893800 259 93 233 ,6 333333 N A F 0 m w R 6% m n n 9 M aaf 6 A .m H s t OLQVJBO r' mn N m e m mumm i W U b N Mmo I... e 0% wm i i CE WDFM T E 5 T o O t H mm W FA h N 7 Primary Examiner-Henry T. Klinksiek [73] Asslgnee' Lodegglgaitlgpfiglrerggiggg 7 u Attorney, Agent, or Firm--William J. Daniel Construction de Moteurs d Aviation, Paris, France [57] ABSTRACT A fuel metering device comprises a metering needle guided cantilever fashion in a bore and operated by a double [22] Filed: Apr. 17, 1973 [21] Appl. No.: 352,003 r -acting actuator so as to regulate the passage cross-section of a regulating aperture which deter mines the flow rate under pressure of a fuel containing or possibly containing solid impurities. The control consists of a piston integral with a shaft of the needle France......,................ 72.13605 and sliding inside a cylinder, and the bore is made through a partition separating this cylinder from a 32 i 7 BW l 51% 2 $100 W 3 1 8 m mm "T m m 7" 3 1 1" mmh u r "8 ue L C 0 d Std I ll UhF 1]] 2 00 555 [ll chamber receiving the regulated fuel flowing out of the regulating aperture. The two chambers of the cylinder are fed, at modulated pressures, with filtered fuel, and the bore is provided with an annular groove [56] References Cited UNITED STATES PATENTS which is fed with fuel taken through a filter upstream of the metering device 2,980,139 4/1961 3.018622 1/1962 Werts.......... 3,032,077 5/l962 Plock et PATENTED 4 75 FUEL METERliNG DEVICE ESPECIALLY FOR THE COMBUSTllON CHAMBER OF AN AEROJET ENGllNE The invention relates to a fuel metering device of the type comprising a metering unit such as a needle guided in a bore and able to slide under the action of a control device so as to regulate the passage crosssection of an aperture which determines the flow of fuel feeding, for example, the combustion chamber of an aerojet engine.

Known metering devices of this type have the draw back of being sensitive to pollution of the fuel by solid impurities, such as particles of metal, which may interfere with the sliding of the needle inside the bore which guides it and can even cause total seizing up of the needle and unserviceability of the metering device.

The object of the present invention is the provision of a fuel metering device suitable for the precision regulation of the flow rate of fuel which contains or may contain solid impurities. This metering device may also be miniaturised, i.e. its dimensions can be greatly reduced. It may be noted that the three above conditions (precise flow regulation, use of a polluted fuel and possibility of miniaturisation) appear at first to be irreconcilable. The applicants have, however, succeeded in reconciling them by achieving extremely precise needle guidance, i.e. almost without play, associated with a compact device which prevents the access of impurities to this guidance.

To this end, a metering device according to the invention, comprising a metering needle cantilever guided in a bore and operated by a double-acting actuator so as to regulate the passage cross-section of a regulating aperture which determines the flow rate of a fuel under pressure containing or possibly containing solid impurities, is characterised in that the actuator consists of a piston integral with the shaft of the needle and sliding inside a cylinder, that the bore is made through a partition separating this cylinder from a chamber receiving the regulated fuel flowing from the regulating aperture, that the two chambers of the cylinder are fed, at modulated pressures, with fuel taken through a filter upstream of the metering device, and that the bore is provided with an annular groove which is likewise fed with fuel taken upstream of the metering device through the filter or through another filter.

it is due to the combination of these various measures that it is possible to construct a miniaturised metering device capable of regulating, with precision, the flow of polluted fuel. In fact, these measures act together so as to enable reduction of the length of the metering device and to ensure precise guidance of the needle in spite of the presence of impurities in the fuel. As the needle is guided by the bore made in the partition which separates the cylinder from a chamber of the metering device where polluted fuel is flowing, it is not necessary to provide for guidance on the part of the cylinder opposite to this chamber. Since this chamber is located downstream of the regulating aperture, the pressure prevailing there is less than that of the polluted fuel upstream of the metering device and it is therefore possible, by taking fuel upstream of the metering device and filtering it, to have available a lubricant at a pressure higher than that of the chamber so as to create a seal preventing the polluted fuel from blocking the guidance of the needle. However, the pressure of the fil- 2 tered fuel which feeds the cylinder chamber adjacent the bore is modulated and in certain circumstances risks being lower than that of the chamber located downstream of the regulating aperture, thus the seal is formed by fuel taken through a filter above the metering device and feeding an annular groove in the bore.

In effect, it will be understood that this filtered fuel, being at a higher pressure than that of the regulated fuel (which has undergone a pressure drop while passing through the regulating aperture) tends to flow into the bore around the needle, from the annular groove towards the regulated fuel chamber, and constitutes an efficient seal against access of the impurities from the latter to the clearance between the bore and the needle. A flow is thus produced from the annular groove towards the chamber adjacent the cylinder, since its pressure is modulated and therefore lower than that of the filtered fuel feeding the groove.

According to a preferred feature of the invention, the filter consists of a sleeve with a filtering wall which is traversed internally by the fuel feeding the metering device and which is enclosed in a cavity from where the filtered fuel is taken. The inside surface of the sleeve, which forms the entry face of the filter, is thus perm anently washed by the fuel feeding the metering device at a large flow rate, and consequently does not run the risk of becoming clogged.

According to another feature of the invention, the pressure of the filtered fuel in the cylinder chambers is modulated by an escape device placed in a cavity receiving fuel through an aperture the passage crosssection of which is regulated, differentially with that of the regulating aperture, by the free end of the metering needle, the cavity being linked to a fuel return ducting system.

The description which follows with reference to the accompanying drawing is given by way of nonlimitative example, and explains how the invention can be put into practice. All features which emerge both from the text and from the drawing are within the scope of the present invention. The drawing is a partial sectional view of an aero-turbojet engine regulator, comprising a fuel metering device according to the invention.

The metering device, part of which is shown in the drawing, is intended to regulate the feed flow in a duct I linked to the injectors, not illustrated, of the combustion chamber of the jet engine, of fuel taken in at 2 by a fuel pump 3.

The polluted fuel, i.e. containing or liable to contain solid impurities, it taken in at 2 by the fuel pump 3, which is of the vane type and is therefore functionally unimpaired by impurities. The pump delivers the fuel via inlets 3a,3b to two ducts 441,41) flowing into a channel 4 terminating at the inlet 5 to a metering device according to the invention, which is designated as a whole by the reference 6. The delivery duct 4a comprises a section the wall of which consists of a porour sleeve 7a and which is enclosed in a cavity 7b forming, together with the sleeve 7a, a filter 7 according to the invention. From the cavity 7b exits a duct 8 which thus receives fuel taken in from the duct 4a through the sleeve 7a and consequently filtered and which feeds devices which will be described later. These devices consume a very small amount of fuel; moreover. the filtering sleeve 7a does not risk becoming clogged since. as has already been stated, its entry surface is permanently washed by the fuel circulating at a high rate in the duct 4a, so that the pressure drop by the fuel when passing through the filter is negligable and the pressure obtaining in the duct 8 is almost equal to the pressure in the channel 4.

The metering device 6 comprises a needle 9 provided with a cylindrical shaft 9a which slides in a bore 10 under the action of a control device 11, which will be described later, in such a way as to modify in opposite senses the cross-sectional area of two apertures 12 and 13 respectively providing communication between the inlet 5 of the metering device and its outlet 14 and with a cavity 15 which communicates with a return fuel channel 16 which by-passes the pump 3. The outlet 14 of the metering device opens into a duct 17 which can be made to communicate with the duct 1 in order to feed the injectors by a poppet valve device, represented as a whole by the reference 18, which does not form part of the present invention. The opening and closing of this poppet valve device 18 can be controlled manually by means of a three-way cock 19 which allows a control chamber 18a of this device to communicate with either the duct 8 or the cavity 15. Closing this poppet valve device places the duct 1 in communication with a drainage duct 18b.

The channel 4 feeding the metering device 6 from the pump 3 is also linked by a regulating valve 20, which also does not form part of the invention, to a fuel return duct 21 by-passing the pump. According to a well known principle, this regulating valve varies the flow communication between the channel 4 and the duct 21 in such a way as to maintain constant the pressure drop A p between the inlet 5 and the outlet 14 of the metering device 6. To this end a A p detector 22 modulates, as a function of A p, the fuel pressure downstream of a throttle 23a in a duct 23 which takes fuel from the channel 4 through a filter 23b analogous to the filter 7, and the modulated pressure is applied to a bellows 24 in order to control the position of a needle 25 forming the flow control unit of the regulating valve 20.

The poppet valve device 18 is opened when the engine is started and is closed only when it is stopped; it stays open throughout the period of operation and the metering device 6 regulates the flow of fuel C which is supplied to the injectors, not illustrated, through the ducts l7 and 1. The active part of the needle 9 comprises two portions with surfaces inclined in opposite directions 12a,13a, having approximately the shape of two truncated cones joined side by side at their base, which control respectively the passage sections of an annular aperture 12 allowing passage of the regulated flow C and of an annular passage 13 through whch the surplus flow entering the metering device at 5 is bypassed into a cavity 15 and from there into the return duct 16. As the pressure drop A p undergone by the fuel when passing through the regulating annular aperture 12 is kept constant by the regulating valve 20, the flow C passing through the aperture 12 is proportional only to the passage cross-section of the latter, and it is known that the surface portion 12a can be given such a shape that the flow C is directly proportional to a distance x corresponding to the position of the needle 9 from a left-hand limit position. In what follows it will be assumed that this condition is achieved in the construction represented.

The control system 11 of the metering device comprises a cylinder 26 in which a piston 27, integral with shaft 9a of needle 9, slides. A by-pass 28 of the filtered fuel duct 8 divides into two branches 28a, 28b respectively feeding, through restrictors 29a,29b, the two chambers 26a,26b of the cylinder separated by piston 27. The pressures in these two chambers are modulated, according to the various regulation parameters of the engine, by a force balance apparatus designated generally by the reference 30.

This apparatus 30 comprises two levers 31,32 which hold between them a pair of rollers 33. The first lever 31, pivoted at 31a, is acted upon in opposite directions by two bellows 34,35 adjusted in such a way that the resulting effort is proportional to a pressure P,4, which is the output pressure of the high-pressure compressor (not illustrated) of the engine, the inside of one of these bellowsbeing subjected to this pressure P,,4 whilst the inside of the other bellows is subjected to a vacuum in order to compensate for the action of the ambient pressure. The second lever 32 comprises, at the other side of its pivot 32a, an arm 32b which is subject to the action of a spring 36 resting on a boss 9b formed at the end of the needle 9 of the metering device 6. The end of the first lever 31 forms a vane which moves between two opposed nozzles 37a,37b linked respectively by ducts 38a,38b to the two chambers 26a,26b of the cylinder 26. The piston 27 of the metering device thus acts as a servo-piston controlled by the pressures of these two chambers modulated by the nozzles and the vane, the lever 32 forming together with the spring 36 a feedback loop.

A specific value of the ratio x/P 4, and consequently a specific value of the ratio C/P,4, thus corresponds to every instantaneous position of the double roller a rrangement 33. The roller arrangement 33 is supported by a rod 39 which extends in the general direction of the levers 31 and 32 and which is pivoted at the end of a control lever 40 carrying a roller 40a actuated by a cam 41, the position of which is controlled by a motor 42. The position of the double roller arrangement 33 is thus determined by the motor 42 which is itself controlled by an electronic computer (not illustrated) according to various parameters such as temperatures, rotation speeds, etc. A pick-up 43, coupled to the motor 42 by gears 43a, induces the position of the cam 41 in the motor 42 through reaction.

The fuel flow C supplied by the metering device 6 to the duct 17 and therefore to the injectors (not illustrated) is thus a pre-determined funtion of P 4 and the other parameters introduced into the regulation by the computer (not illustrated).

The bore 10, which guides the cylindrical shaft 9a of the needle 9 during its sliding movement, is made through a partition 44 separating the cylinder 26 from a chamber 45 which received the regulated fuel from the aperture 12 and discharges it through the outlet 14. In this partition 44 is an annular groove 46 communicating by channels 47 with a small annular collector 48 which itself communicates by a channel 49 with the duct 8. As stated earlier, the pressure of the filtered fuel in the duct 8 is almost equal to the pressure in the ducting system 4, which is higherby the quantity A p than the pressure in the chamber 45. The filtered fuel therefore tends to flow from the annular groove 46 towards chamber 45 and prevents the impurities contained in the unfiltered fuel circulating in this chamber from penetrating into the clearance between the shaft 9a and the bore 10, so that there is no risk of this shaft jamming in the bore. Neither is there a risk of the piston 27 jamming, since the fuel filling the cylinder 26 is filtered.

It should be noted that the only systems which are filtered, namely, those of ducts 8 and 23, are low flow rate systems. As there is no risk of filters 7 and 23b becoming clogged, as has been explained above, it is not necessary to make provision for a clogging indicator or for periodic inspections. It is also not necessary to make provision in the aircraft for inspection doors for access to the filters. Although fine filters tend to ice up, there is no risk of this happening with the filters 7 and 23b because of the large flow rate of fuel which sweeps their inlet surfaces.

We claim:

1. In a flow metering device for fuel containing or liable to contain solid impurities which comprises inlet and outlet chambers (5,45) connected by a regulating port (12), feed intake means (3,3a,3b,4) for supplying under pressure said fuel to said inlet chamber for passage through said port into said outlet chamber, fuel outlet means (17,1) for delivering said fuel from said outlet chamber, a flow metering needle (9) movable axially through said regulating port (12) to vary the cross-sectional area of said port and thus the rate of fuel flow therethrough, a partition (44) at one side of said inlet and outlet chambers and having a bore (10) therein coaxial with said needle, an integral extension (9a) on said needle (9) slidably fitted in said partition bore (10) for axial movement therein, and control means (11) operatively associated with said needle extension to move the same axially in said partition bore, the improvement comprising an annular groove (46) formed in the surface of the bore (10) intermediate the ends thereof, and means (7,8,49) communicating with said fuel intake means for withdrawing therefrom a small secondary flow of fuel, filtering said small secondary flow, and delivering the same to said annular groove (46) under a pressure higher than the pressure of the unfiltered fuel acting on said partition (44) whereby the entry of said impurities into the clearance space between said bore (10) and said needle extension is prevented.

2. The metering device of claim I wherein said control means comprises a cylinder (26) on the side of said partition (44) opposite said inlet and outlet chambers, a piston (27) sliding in said cylinder (26) and dividing the same into first and second control chambers (26a,26b), said piston being connected to said needle extension (9a) for movement therewith, and conduit means (28,28a, 28b,29a,29b) for supplying said control chambers with said filtered fuel.

3. A fuel metering device of claim 2 including piston actuating means comprising first and second passages (28a,28b) each comprising restriction means (29a,29b) and leading from said filtered fuel delivering means (8) to said first and second control chambers (26a,26b), respectively, to feed the same with said filtered fuel, and an escape device (30) for differentially controlling leakages of filtered fuel out of said first and second control chambers to modulate the pressures thereon acting on the opposite sides of piston (27).

4. The flow metering device of claim 3 comprising a cavity (15), a further port (13) providing communication between said inlet chamber (5) and the cavity (14), said flow metering needle (9) being movable relative to the further port (13) to control the crosssectional area thereof differentially with the crosssectional area of said regulating port (12), and means (16) connecting the cavity toa fuel return ducting system, said escape device being contained within said cavity to discharge said leakages therein.

5. The flow metering device of claim 1 wherein said means for withdrawing and filtering said secondary flow of fuel comprises a conduit (3a) including a porous wall portion (7a) forming a filtering sleeve, and a cavity (7b) surround the porous wall portion (7a) to receive the fuel filtering therethrough, whereby said porous wall portion is washed by the unfiltered fuel flowing through the conduit including the same to remove impurities retained thereby and reduce clogging. l l l= =l= 

1. In a flow metering device for fuel containing or liable to contain solid impurities which comprises inlet and outlet chambers (5,45) connected by a regulating port (12), feed intake means (3,3a,3b,4) for supplying under pressure said fuel to said inlet chamber for passage through said port into said outlet chamber, fuel outlet means (17,1) for delivering said fuel from said outlet chamber, a flow metering needle (9) movable axially through said regulating port (12) to vary the cross-sectional area of said port and thus the rate of fuel flow therethrough, a partition (44) at one side of said inlet and outlet chambers and having a bore (10) therein coaxial with said needle, an integral extension (9a) on said needle (9) slidably fitted in said partition bore (10) for axial movement therein, and control means (11) operatively associated with said needle extension to move the same axially in said partition bore, the improvement comprising an annular groove (46) formed in the surface of the bore (10) intermediate the ends thereof, and means (7,8,49) communicating with said fuel intake means for withdrawing therefrom a small secondary flow of fuel, filtering said small secondary flow, and delivering the same to said annular groove (46) under a pressure higher than the pressure of the unfiltered fuel acting on said partition (44) whereby the entry of said impurities into the clearance space between said bore (10) and said needle extension is prevented.
 2. The metering device of claim 1 wherein said control means comprises a cylinder (26) on the side of said partition (44) opposite said inlet and outlet chambers, a piston (27) sliding in said cylinder (26) and dividing the same into first and second control chambers (26a,26b), said piston being connected to said needle extension (9a) for movement therewith, and conduit means (28,28a, 28b,29a,29b) for supplying said control chambers with said filtered fuel.
 3. A fuel metering device of claim 2 including piston actuating means comprising first and second passages (28a,28b) each comprising restriction means (29a,29b) and leading from said filtered fuel delivering means (8) to said first and second control chambers (26a,26b), respectively, to feed the same with said filtered fuel, and an escape device (30) for differentially controlling leakages of filtered fuel out of said first and second control chambers to modulate the pressures thereon acting on the opposite sides of piston (27).
 4. The flow metering device of claim 3 comprising a cavity (15), a further port (13) providing communication between said inlet chamber (5) and the cavity (14), said flow metering needle (9) being movable relative to the further port (13) to control the cross-sectional area thereof differentially with the cross-sectional area of said regulating port (12), and means (16) connecting the cavity toa fuel return ducting system, said escape device being contained within said cavity to discharge said leakages therein.
 5. The flow metering device of claim 1 wherein said means for withdrawing and filtering said secondary flow of fuel comprises a conduit (3a) including a porous wall portion (7a) forming a filtering sleeVe, and a cavity (7b) surround the porous wall portion (7a) to receive the fuel filtering therethrough, whereby said porous wall portion is washed by the unfiltered fuel flowing through the conduit including the same to remove impurities retained thereby and reduce clogging. 